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Bio; Lecture 05; Evolution

Bio; Lecture 05; Evolution - Principles of Biology...

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Principles of Biology Bio U103 1-18-07 Evolution Three prerequisites of Natural Selection o Organisms must over-reproduce Therefore, must compete for resources o Characteristics must be inherited from parents o Organisms are not identical--Variability There are 40 to 180x10^6 sperm in one ejaculate The probability of having 2 identical sperm considering independent assortment alone as the source of genetic variation is 1 in 8x10 6 Considering crossing over and mutations, the probability of having 2 identical offspring from 2 different pregnancies is basically 0. Variability is important because if there is a major change in the environment, there should be some variants of a species that are able to adapt to the change and survive. Selection pressures (biotic and abiotic) o Selection pressures : pressures from the environment that cause some individual organisms to live and some to survive. o They act on the different phenotypes (physical characteristics) and affects the genetic composition of the genetic makeup of the population by picking out unfavorable traits. o Abiotic selection pressures: Temperature, humidity, light, water content, nutrients, natural disasters, etc. o Biotic selection pressures: Interactions amongst living organisms: predators, parasitism, disease, competition, mates Evolution by Natural Selection Requires: o Traits to be inherited o Genetic variability within the population o
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